This invention relates to electrical conduit, and more particularly to conduit fittings, including couplings and connectors, and a method for making junctions to and between metal conduit.
Electrical conduit forms the backbone of the wiring system in many buildings, both commercial and residential. It is generally believed to be the highest quality and safest installation mechanism, because the wires which carry the electrical current throughout the structure are totally enclosed within the conduit system.
Metal conduit can be of several varieties, including Electrical Metallic Tubing (EMT), Intermediate Metallic Conduit (IMC) and rigid conduit. Such conduit comes in standard lengths such as ten feet, can be secured in place and bent to form corners, all in customizing the electrical backbone system for a building. Sections are readily cut by ordinary hand tools and bent with special conduit benders to fit a particular application.
EMT conduit sections have no fittings at the ends. IMC and rigid conduit sections are manufactured with threaded ends. However, when the particular application requires the conduit section to be cut to a shorter length, all three forms of conduit will have at least one unthreaded end with no fittings.
Thus when joining the conduit end to end, a fitting known as a coupling is required to join the sections. Also when joining a section of conduit to a fixture, a distribution box, a junction box or the like, a fitting known as a connector is necessary. The fitting is secured to the conduit at one end and to the fixture or other device at the other end. These types of conduit fittings are known generally as threadless fittings.
In the past, three types of threadless fittings have been available for making junctions and securing conduit to fixtures and the like. Each has its limitations. First is the indenter type, which has a sleeve that fits over the conduit and then is crimped using a special hand tool. This type of fitting is not much used today and requires use of a special tool.
The second type of fitting is a compression fitting. This fitting generally has a sleeve with threads on the outside, a gland and a nut. As the nut engages the threads and tightens, it presses the gland in between the sleeve and the conduit. The gland compresses around the conduit and engages the outer surface of the conduit and the inner surface of the sleeve to make a secure junction. Unfortunately, in order to fit this type of fitting to a section of conduit requires the use of two pairs of channel pliers, which can sometimes be awkward.
The third type of fitting, and the one commonly used today, is the set screw type arrangement. The end of a conduit section is slipped into a pocket in the fitting, and a set screw tightened to get a reasonably good mechanical joint between the fitting and the conduit. In a coupling for end to end connections, two pockets and two set screws would be provided, one for each section of conduit. In a connector for junction box applications, one end would be threaded to accept a conventional lock nut, while the other end would have the pocket and set screw as described above. The problems with set screw type fittings are the possibility of not tightening the screw as an oversight or the set screw loosening, which tend to reduce the integrity of the overall conduit system. An installation problem that is present is even more significant. Usually an electrician when setting up a conduit run will extensively use a pair of channel type pliers for fitting the items together. But whenever a connection needs to be made, the electrician must then put the channel pliers back in his pouch and take out a screwdriver to make the connection. This constant switching between tools, while it would not seem to be terribly significant, can result in a significant loss of efficiency and time in making a large installation.
In view of the foregoing, it is a general aim of the present invention to provide a fitting system for conduit which not only provides for a secure conduit installation, but which simplifies the installation task.
In that regard, a more detailed object is to provide a conduit fitting having a lock mechanism which is simpler and less complex than those provided heretofor.
It is a feature of the invention that the fittings typically used with EMT conduit, can also be used with the other forms of metallic conduit, such as IMC and rigid conduit, which when manufactured have threaded ends but when cut for a particular application have unthreaded smooth ends without fittings.
With respect to the method aspects of the invention, an object is to provide a method for connecting a conduit section into a conduit assembly which can, if desired, be accomplished with a single tool.
In accomplishing its aims and objectives, the invention provides a fitting for metallic conduit which comprises a body having an annular pocket with a central axis, the pocket being dimensioned to slide onto a smooth end of a conduit section. The body has an opening and a cam support on the body adjacent the opening. A cam lock is pivotably fixed in the cam support. The cam lock has a cam surface on one end and an opposite end for rotation of the cam surface about the pivot point. The cam lock is pivotable in the earn support between (i) a locked position in which the cam surface protrudes through the opening sufficiently to deform the surface of a conduit section when inserted and thereby lock the fitting and conduit section together, and (ii) an unlocked position in which the cam is withdrawn sufficiently into the opening to allow insertion or removal of the conduit from the annular pocket.
It is a feature of certain embodiments that the cam lock also has an intermediate position in which the cam surface protrudes through the opening but not so far as in the locked position. It protrudes sufficiently far to engage a conduit section when positioned in the pocket for preliminarily locking the fitting and conduit section together.
It is a further feature that the cam lock has at least one projection, and in some cases multiple serrations, positioned to engage the surface of a conduit section when being locked in the fitting. The projection or serrations tend to render the locking action more positive.
The invention also has method aspects which involve using a single tool to connect a conduit section into a conduit assembly. The method includes the steps of providing a conduit fitting which has a cam lock arrangement with a pivot lock having a cam surface on one end for locking/releasing the conduit section, and an operating lever on the other end. The conduit is inserted into the fitting to the appropriate position. The method also involves holding the conduit and fitting in the appropriate position and moving the operating lever to achieve a preliminary grip on the conduit. Finally, the method involves clamping the operating lever toward the fitting body to drive the cam into the conduit surface thereby to lock the fitting and conduit together.
Preferably the inserting and clamping steps utilize a single tool, generally a pair of channel pliers normally used by electricians installing conduit.
These and other objects advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.